1. Field of the Invention
The present invention relates generally to a hybrid electric vehicle (HEV). More particularly, the present invention relates to an apparatus and method for controlling command torques in a hybrid electric vehicle.
2. Description of Related Art
A hybrid electric vehicle (HEV) refers to a next-generation motor vehicle which, by means of combined mounting of an internal combustion engine and a motor engine, significant reduction of a body's weight and minimization of air resistance, substantially reduces fuel consumption and an amount of harmful gas emissions as compared with existing ordinary vehicles. The HEV can reduce the amount of harmful gas emissions by 90% or more over existing vehicles, thus being capable of decreasing air pollution and improving the surrounding environment of an urban area as well as fitting in with traffic control, road plan and so on. For this reason, the HEV is called an “eco-car”.
The HEV is driven with high fuel-efficiency and has combination of advantages as it has both a gasoline engine and an electric engine. Therefore, its vital function is that it can be switched between its internal combustion engine and its motor engine so as to be suitable for the road and surrounding environment. In this manner, the HEV, making use of both the internal combustion engine and the motor engine as a power source, has been developed in every country for a long time. Today there are just a few mass-produced hybrid vehicles in the world. In the future, there is a strong possibility that many companies will launch into the HEV market. However, the HEV may have a different system due to a difference between two design concepts of “advancement of the internal combustion engine” and “development of the electric car.”
FIG. 1 shows the structure of the power train of an ordinary hard type HEV. As shown in FIG. 1, the structure of the power train of an ordinary hard HEV includes an internal combustion engine 1 generating rotating power, an engine clutch 2 connected to an output of the internal combustion engine 1, carrier gear 3 connected to the engine clutch 2, a ring gear 4 connected to the carrier gear, a driving motor 5 generating rotating power and connected to the ring gear 4, a sun gear 6 connected between the carrier gear 3 and the ring gear 4, a generator 7 connected to the sun gear 6, and a battery 8 (shown in FIG. 2) supplying power to the driving motor 5.
The driving motor 5 and generator 7 has a structure of ISG (Integrated Starter & Generator).
The HEV having this power train structure has different travel modes selected on the basis of its speed during traveling.
FIGS. 2a through 2e show travel modes of an ordinary HEV. As shown in FIG. 2a, when departing or during low-speed traveling, the HEV is driven by the driving motor 5 supplied with power from the battery 8. As shown in FIG. 2b, when in normal motion, the HEV is driven in the travel mode where the internal combustion engine 1 and the driving motor 5 combine to provide optimal fuel economy. As shown in FIG. 2c, when accelerating or hill-climbing, the HEV is driven by the aid of power from the driving motor 5. As shown in FIG. 2d, when decelerating, the HEV collects energy by using the driving motor 5 as a generator to charge the battery 8. As shown in FIG. 2e, when stopping, the HEV stops the engine to lessen unnecessary fuel consumption and emission of exhaust gases.
The HEV is equipped with a hybrid control unit (HCU). The HCU is adapted to set and output speeds and torques of the engine, generator and motor so as to enable the HEV to be driven at optimal system setting.
However, in the conventional HCU, when calculation by which its own torque is set is abnormal, information on command torques is beyond an appropriate range, which results in breakage of a hybrid dynamic system, and so on.
In this regard, there is disclosed U.S. Pat. No. 6,490,511. In this document, a driver demand torque is set for a main controller for an HCU, and then compared with an output shaft torque estimated at an independent plausibility check (IPC). When the estimated output shaft torque is greater than the driver demand torque, the vehicle stops driving. Thereby, the command torque information maintains an appropriate range.
However, the technique disclosed in U.S. Pat. No. 6,490,511 has the following problems:
1. There is neither a signal diagnosis of inputs nor a limp-home strategy of faults (typically, in the case of using redundant sensors, a fault management approach used when any one of the sensors is out of order), wherein the inputs and faults have an influence on setting of the driver demand torque of the main controller for the HCU.
2. The HCU merely sets torques of the engine, motor and generator, and an actually obtained torque of each of the engine and motor is a monitoring target of each of the engine and motor, thus being discriminated from a function of the HCU. Moreover, an estimated output torque in the IPC may have an incorrect value, so that the estimated output torque is not required. Hence, it is sufficient only to check whether a target torque of each of the engine and motor based on the driver demand is exactly achieved or not.
3. Even when an input of the main controller of the HCU causes trouble, there is no limitation to the setting of the driver torque. In this case, a torque monitoring function may be insufficient.
4. There is no concrete countermeasure against an abnormal torque. In the case of the existing HEV, a system reaction takes place by vehicular shut-off, which is merely effective for extreme cases. Thus, the system reaction should be varied according to different abnormal function types.
5. It is checked whether to meet output torque relation by a planetary gear which is mainly used in the hard type HEV. In this case, when the abnormal torque is output, it is impossible to prevent damage of hardware.